The present invention relates generally to smart cards, and more specifically relates to an improved dual mode smart card module, an improved dual mode smart card incorporating such a module, and a method of forming the same.
Dual mode smart cards incorporate contacted and contactless interfaces into a single card. Dual mode smart cards typically include a module which is disposed in a recess in a card body. The module typically includes a double sided substrate having a metalized layer on each side, and an integrated circuit wafer or die coupled to the substrate, such as by wire leads. A protective coating or encapsulant covers the die. Antenna leads or pads for the contactless application are provided which are not covered by the protective coating. The protective coating is typically applied using the xe2x80x9cglob topxe2x80x9d process.
Existing modules, such as is shown in FIGS. 3 and 4, incorporate a 200 micron thick substrate and a 410 micron thick protective coating, giving a total module thickness of 610 microns. The total card thickness is typically specified at 762 microns xc2x176 microns, resulting in a card measuring 686 microns thick at the low end of the tolerance. The recess which receives the module is typically 635 microns deep, with a 25 micron tolerance for milling the recess in the card body. Thus, the bottom wall of the recess will have a thickness of 51 microns. Unfortunately, such a thin bottom wall measuring about 51 microns increases distortion during the hot melt bonding used to secure the module to the card body. Moreover, such a thin bottom wall frequently tears during milling when forming the recess in the card body.
The glob topping process requires that a dam be dispensed around the die prior to application of the protective coating. The dam occupies a significant amount of surface area on the surface of the substrate, and thus less surface area is available for bonding the module to the card body. Using the glob topping process, the available surface area is typically limited to about 83.2 square millimeters, which may not be sufficient to optimize the strength of the bond and which ultimately may lead to long term field reliability problems. Attempts have been made to employ thinner, metal rings as dams around the die in order to increase the available bonding area, but in practice such metal rings place the antenna pads too close to the metal rings, requiring much tighter tolerances which raises production costs.
Accordingly, there is a need for an improved dual mode smart card module and for an improved dual mode smart card incorporating such a module.